Several other Leguminous genera produce cleistogamic flowers, as may be seen in Table 8.38; but much does not appear to be known about them. Von Mohl says that their petals are commonly rudimentary, that only a few of their anthers are developed, their filaments are not united into a tube and their pistils are hook-shaped. In three of the genera, namely Vicia, Amphicarpaea, and Voandzeia, the cleistogamic flowers are produced on subterranean stems. The perfect flowers of Voandzeia, which is a cultivated plant, are said never to produce fruit (8/13. Correa de Mello ‘Journal of the Linnean Society Botany’ volume 11 1870 page 254, particularly attended to the flowering and fruiting of this African plant, which is sometimes cultivated in Brazil.); but we should remember how often fertility is affected by cultivation.
Impatiens fulva.
Mr. A.W. Bennett has published an excellent description, with figures, of this plant. (8/14. ‘Journal of the Linnean Society Botany’ volume 13 1872 page 147.) He shows that the cleistogamic and perfect flowers differ in structure at a very early period of growth, so that the existence of the former cannot be due merely to the arrested development of the latter,—a conclusion which indeed follows from most of the previous descriptions. Mr. Bennett found on the banks of the Wey that the plants which bore cleistogamic flowers alone were to those bearing perfect flowers as 20 to 1; but we should remember that this is a naturalised species. The perfect flowers are usually barren in England; but Professor Asa Gray writes to me that after midsummer in the United States some or many of them produce capsules.
Impatiens noli-me-tangere.
I can add nothing of importance to Von Mohl’s description, excepting that one of the rudimentary petals shows a vestige of a nectary, as Mr. Bennett likewise found to be the case with I. fulva. As in this latter species all five stamens produce some pollen, though small in amount; a single anther contains, according to Von Mohl, not more than 50 grains, and these emit their tubes while still enclosed within it. The pollen-grains of the perfect flowers are tied together by threads, but not, so far as I could see, those of the cleistogamic flowers; and a provision of this kind would here have been useless, as the grains can never be transported by insects. The flowers of I. balsamina are visited by humble-bees (8/15. H. Muller ‘Die Befruchtung’ etc. page 170.), and I am almost sure that this is the case with the perfect flowers of I. noli-me-tangere. From the perfect flowers of this latter species covered with a net eleven spontaneously self-fertilised capsules were produced, and these yielded on an average 3.45 seeds. Some perfect flowers with their anthers still containing an abundance of pollen were fertilised with pollen from a distinct plant; and the three capsules thus produced contained, to my surprise, only 2, 2, and 1 seed. As I. balsamina is proterandrous, so probably is the present species; and if so, cross-fertilisation was effected by me at too early a period, and this may account for the capsules yielding so few seeds.
Drosera rotundifolia.
The first flower-stems which were thrown up by some plants in my greenhouse bore only cleistogamic flowers. The petals of small size remained permanently closed over the reproductive organs, but their white tips could just be seen between the almost completely closed sepals. The pollen, which was scanty in amount, but not so scanty as in Viola or Oxalis, remained enclosed within the anthers, whence the tubes proceeded and penetrated the stigma. As the ovarium swelled the little withered corolla was carried upwards in the form of a cap. These cleistogamic flowers produced an abundance of seed. Later in the season perfect flowers appeared. With plants in a state of nature the flowers open only in the early morning, as I have been informed by Mr. Wallis, who particularly attended to the time of their flowering. In the case of D. Anglica, the still folded petals on some plants in my greenhouse opened just sufficiently to leave a minute aperture; the anthers dehisced properly, but the pollen-grains adhered in a mass to them, and thence emitted their tubes, which penetrated the stigmas. These flowers, therefore, were in an intermediate condition, and could not be called either perfect or cleistogamic.
A few miscellaneous observations may be added with respect to some other species, as throwing light on our subject. Mr. Scott states that Eranthemum ambiguum bears three kinds of flowers,—large, conspicuous, open ones, which are quite sterile,—others of intermediate size, which are open and moderately fertile—and lastly small closed or cleistogamic ones, which are perfectly fertile. (8/16. ‘Journal of Botany’ London new series volume 1 1872 pages 161- 4.) Ruellia tuberosa, likewise one of the Acanthaceae, produces both open and cleistogamic flowers; the latter yield from 18 to 24, whilst the former only from 8 to 10 seeds; these two kinds of flowers are produced simultaneously, whereas in several other members of the family the cleistogamic ones appear only during the hot season. According to Torrey and Gray, the North American species of Helianthemum, when growing in poor soil, produce only cleistogamic flowers. The cleistogamic flowers of Specularia perfoliata are highly remarkable, as they are closed by a tympanum formed by the rudimentary corolla, and without any trace of an opening. The stamens vary from 3 to 5 in number, as do the sepals. (8/17. Von Mohl ‘Botanische Zeitung’ 1863 pages 314 and 323. Dr. Bromfield ‘Phytologist’ volume 3 page 530, also remarks that the calyx of the cleistogamic flowers is usually only 3-cleft, while that of the perfect flower is mostly 5- cleft.) The collecting hairs on the pistil, which play so important a part in the fertilisation of the perfect flowers, are here quite absent. Drs. Hooker and Thomson state that some of the Indian species of Campanula produce two kinds of flowers; the smaller ones being borne on longer peduncles with differently formed sepals, and producing a more globose ovary. (8/18. ‘Journal of the Linnean Society’ volume 2 1857 page 7. See also Professor Oliver in ‘Natural History Review’ 1862 page 240.) The flowers are closed by a tympanum like that in Specularia. Some of the plants produce both kinds of flowers, others only one kind; both yield an abundance of seeds. Professor Oliver adds that he has seen flowers on Campanula colorata in an intermediate condition between cleistogamic and perfect ones.
The solitary almost sessile cleistogamic flowers produced by Monochoria vaginalis are differently protected from those in any of the previous cases, namely, within “a short sack formed of the membranous spathe, without any opening or fissure.” There is only a single fertile stamen; the style is almost obsolete, with the three stigmatic surfaces directed to one side. Both the perfect and cleistogamic flowers produce seeds. (8/19. Dr. Kirk ‘Journal of the Linnean Society’ volume 8 1864 page 147.)
The cleistogamic flowers on some of the Malpighiaceae seem to be more profoundly modified than those in any of the foregoing genera. According to A. de Jussieu they are differently situated from the perfect flowers; they contain only a single stamen, instead of 5 or 6; and it is a strange fact that this particular stamen is not developed in the perfect flowers of the same species. (8/20. ‘Archives du Museum’ tome 3 1843 pages 35-38, 82-86, 589, 598.) The style is absent or rudimentary; and there are only two ovaries instead of three. Thus these degraded flowers, as Jussieu remarks, “laugh at our classifications, for the greater number of the characters proper to the species, to the genus, to the family, to the class disappear.” I may add that their calyces are not glandular, and as, according to Kerner, the fluid secreted by such glands generally serves to protect the flowers from crawling insects, which steal the nectar without aiding in their cross-fertilisation (8/21. ‘Die Schutzmittel der Bluthen gegen unberufene Gaste’ 1876 page 25.), the deficiency of the glands in the cleistogamic flowers of these plants may perhaps be accounted for by their not requiring any such protection.